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Given the requirements that a standard Cat 5e cable must live up to, is it possible to transfer data over it faster than the 1 Gbit for maximum 100 meters of cable for 1000BASE-T?

My old ADSL line used the same phone line that my even older 56K modem used, but achieved much higher speeds.

Of course, I realize the switches and/or routers that this Cat 5e cabling is connected to must also be replaced, but that's a lot cheaper than replacing cabling, at least in countries where labor is expensive relative to cost of materials.

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We are getting much closer to the physical limits of twisted pair media nowadays. I doubt you will see the massive increases on the same cable we saw in the transition from dialup to DSL and the transition from 100BASE-TX to 1000BASE-T. We might see some more incremental improvements.

There is talk about new standards for speeds of 2.5 and 5 gigabit per second over twisted pair (google for 2.5 gigabit ethernet to find lots of articles about it) .

http://www.ethernetalliance.org/wp-content/uploads/2013/04/Ethernet-Alliance-Technology-Roadmap-FINAL.pdf indicates that there is an intention to support 2.5 gigabit and maybe 5 gigabit on 100 meters of cat5e.

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So you're almost on the way to answering your own question. It might be possible to push more data down CAT5(e)/CAT6, but the hardware would have to support it.

The question is really not "whats possible" more than "whats feasible". There are already a lot of ways to scale between 1G and 10G. The development cost of hardware to push, let's say, 4G or 8G isn't really worth it as we already have fiber optics that can push 10G over even longer distances.

If the concern is shorter distances of ~100m, and you know that hardware would have to be replaced anyway, fiber is the way to go. Fiber optics are cheap as long as you don't buy major vendor branded transceivers (SFP/XFP) as $1000+ each, you can buy commodity transceivers for a couple hundred bucks - and the hardware to physically support them isn't any different.

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Given the requirements that a standard Cat 5e cable must live up to, is it possible to transfer data over it faster than the 1 Gbit for maximum 100 meters of cable for 1000BASE-T?

You have answered your own question without realizing it. 1000BaseT cannot exceed 1Gbps, because 1000Base-T refers to hardware standard (IEEE 802.3ab). IEEE 802.3ab includes specifications for not only the cabling, but also the chips in your NIC, which terminate the cabling.

Now can someone else come along and create a protocol standard for Cat5e, which exceeds 1Gbps? That's possible, but we can only speculate about the future.

My old ADSL line used the same phone line that my even older 56K modem used, but achieved much higher speeds.

That's because ADSL uses a different protocol standard than old 56k async modems used. ADSL uses signal processing techniques that were foreign to the consumer market when async modems were invented. Those signal processing techniques (and restrictions on distance) give ADSL a big advantage.

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In practice, existing Cat.5e cabling can, on some or all cabling runs, INCIDENTALLY either pass Cat.6 specifications or at least surpass minimal Cat.5e specifications enough to behave within the tolerance margins of 10GBase-T.

The practical limits are dependent on things like when the cable was made - older machinery to make the cable might have been built to only just meet the accuracy needed for Cat.5e, while newer cable might have been produced on the same machinery as the Cat.6a cable and merely labelled differently, either because there was demand for Cat.5e or because cable that marginally fails Cat.6a but meets Cat.5e specs was manufactured due to machine/operator wear/error/maladjustment/contamination...

Also, if a given run works or not can depend on the hardware at both ends - one transceiver design (in a NIC or switch) might be able to just flawlessly work with a marginal cable while another will not.

Small factors like materials aging, someone bending or rolling up the cable, temperature and humidity, someone placing metallic objects too near it ... could be sufficient to turn a working cable run into a non working one suddenly.

Also, the cable could work but create unacceptable EMI problems.

10GBase-T on Cat.5e seems actually common practice - though usually not at maximum length.

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Yes, it is possible, though substandard and not recommended. There exists a 10GBase-T standard ( http://en.wikipedia.org/wiki/10-gigabit_Ethernet#10GBASE-T ) and the equipment is pretty cost efficient, but it requires Cat-6 cabling. But if the distances are not extreme and your cabling was done good, and the patch panels are good and there's no much interference - you may attain 10G speeds on Cat-5e. It worked for me using Intel X520-T cards and 5e cabling at least up to 25ft. Buy a couple of cards off ebay, find a longest path in your cabling system and try these two cards peer to peer (without a switch first). If they establish a link at 10G then try to send some data over for a few hours and see how many errors you'll have in the card statistics. If the stats are OK, transmission speeds are acceptable then you're good to go. Just remember that you're exceeding the standard and taking a risk.

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